Actually cost is the same.
A Yu Jing Hac Tao trooper is 5 GBP, or 4 GBP if you go to the right online stores. A GW mini in a single blister is roughly the same if not more (Special character and points linked GW pricing for example). A really old Warlock model is 4 GBP for 1 a blister, Yriel is 9 GBP!!! And an Autarch 8 GBP.
Hac Tao trooper is just as detailed and lovely sculpt as an autarch and is half the price. I admit that the Autarch comes with a bit of wargear and the infinity trooper doesn't, but come on the choice of a reaper launcher and a shuriken pistol... its hardly huge is it? Oh yes and lets not forget the wings that you most likely wont use.
Also look at the TAGs (the large armoured mecha), these are large all white metal minis, roughly the size of a dreadnought or crisis suit and they are 16 GBP. A plastic GW Dread is 25 GBP and a Tau Crisis commander 15 GBP.